The invention relates to a cast gas turbine blade/vane through which coolant flows, in particular a gas turbine rotor blade with a blade root, which is inserted into a rotatable disk of the gas turbine and which has a plurality of supply ducts for an internal cooling system, and a distribution space. Preferably, it is possible to feed coolant to the supply ducts by way of a feed duct of the disk, wherein the feed duct communicates with the supply ducts via the distribution space. The invention also preferably relates to an appliance, for casting a gas turbine blade/vane, having a casting core which has core ribs forming the supply ducts. Finally, the invention also preferably relates to a method of manufacturing a cast gas turbine blade/vane.
From U.S. Pat. No. 4,344,738, a gas turbine blade/vane is known which is inserted by means of a blade root into a transverse groove of a rotatable disk of the gas turbine, the disk having a feed duct for supplying the gas turbine with coolant. Below the blade/vane root, the feed duct opens into the disk transverse groove intended for accommodating the blade/vane root. Supply ducts, through which the coolant is fed into the internal cooling system, emerge from the blade root. The supply ducts have, in the main, inlet openings with edges.
U.S. Pat. No. 4,992,026 reveals a gas turbine blade/vane through which a coolant flows and which has an internal cooling system, the coolant being introduced by feed ducts into the blade root and fed through supply ducts into the internal cooling system. At their transitions from the blade root, the supply ducts have right-angle edges.
The object of the internal cooling of the gas turbine blade/vane is to prevent severe heating of the blade/vane material, which occurs due to high operating temperatures and can lead to serious damage. For this purpose, it is necessary that the cooling medium should, without difficulty, reach the gas turbine blade/vane parts which, in particular, are remote from the inlet flow region and are exposed to the most severe effects. In the vicinity of the supply duct inlets which, however, have practically no cooling requirement, dead zones occur. Further, the flows depart greatly from the ideal laminar process in the case of inlets, which are greatly constructed with edges, to the supply ducts leading to the internal cooling system, such as is published in U.S. Pat. No. 4,344,738 or U.S. Pat. No. 4,992,026, for example. This, for example, involves an increased danger of the formation of deposits and, in particular, a high flow resistance. It is only possible to force the cooling medium through the supply passages by means of an increased pressure and this is frequently impossible to a sufficient extent.
A further possibility for forming the supply duct region in the lower blade root consists in providing a so-called distribution space from which the supply ducts for the internal cooling system emerge and which is supplied with coolant by the feed duct in the disk. Essentially, the distribution space should serve to provide a reliable and uniform distribution of the coolant to the supply ducts and it is only permissible for small coolant losses to occur. In the usual casting process, this distribution space generally has a rectangular configuration and has, in particular, right-angle transitions between the supply ducts and distribution space. Due to the construction with edges of the inlets to the supply ducts, strong flow eddies occur which, in principle, ensure good cooling of the regions over which flow occurs. Because, however, the distribution space is in the blade/vane root, it is not subject to severe heating effects and has, therefore, only a small cooling requirement.
This state of affairs can be improved by mechanical reworking, after the casting process, of the supply duct inlets from the distribution space. Because of the geometry of the blade root and the properties of the blade/vane material, however, this must generally take place manually and is, in consequence, very labor-intensive. Furthermore, this procedure does not ensure that all the supply ducts of a gas turbine blade/vane have the desired shape and that all the gas turbine blades/vanes of a type have the same flow resistance. This, however, would be necessary for a calculation in advance of the flow properties which would satisfy the high quality requirements and would be necessary for optimum utilization of the cooling medium.
An object of the invention is therefore to provide a cast gas turbine blade/vane, in particular a gas turbine rotor blade, through which coolant flows. It further preferably has transitions from the distribution space to the supply ducts which are optimized in terms of flow, i.e. which has low flow resistance at the outlet openings from the distribution space. An object is to be able to manufacture the distribution space and the internal cooling system in a single manufacturing process, the casting process. A further object of the invention includes providing an appliance and a method for manufacturing such a cast gas turbine blade/vane, through which coolant flows, with a corresponding distribution space.
An object directed toward a cast gas turbine blade/vane through which coolant flows is achieved by a cast distribution space being present which has rounded or beveled inlet openings to the supply ducts, for example.
The rounded or beveled inlet openings to the supply ducts, which are adjacent to the distribution space, ensure that the flow resistance to the cooling medium is minimized, particularly in the transition region between the distribution space and the supply ducts. The cooling medium flow remains substantially laminar. The coolant can thereforexe2x80x94given an appropriate edge-free transition solution from the feed duct to the distribution spacexe2x80x94flow almost unhindered into the distribution space and out of it through the supply ducts. In this way, it reaches the internal cooling system rapidly and with low losses, which leads to a greatly increased service life, particularly in the case of the hot and coolant-intensive regions of the gas turbine blade/vane, for example the leading edge region. The coolant supplied is thus utilized better.
It is no longer necessary for the medium supplied through the feed duct of the disk to be guided round two 90xc2x0 angles into the internal cooling system. On the contrary, it is fed directly to the internal cooling system in a smooth, continuous flow motion. No cavitation, in which the coolant is at rest as in dead zones, occurs while the cooling medium flows round. Because of the rounding or beveling of the inlet openings, the cooling medium supplied is only eddied to a very slight extent.
The inlet openings to the supply ducts abut directly onto the distribution space and are generated with it during one manufacturing process. The rounding or beveling is shaped by the casting process in a reproducible manner. In this way, a series of gas turbine blades/vanes can have the same, predetermined sizes and dimensions for the inlet openings and the distribution space. This provides the basis for a reliable determination in advance of the coolant requirement and/or the coolant function. This is particularly important for ensuring that even remote parts of the gas turbine rotor blades are reliably cooled and that, therefore, the wear due to overheating is minimized.
Due to the present invention, the coolant has already been introduced through the distribution space into the supply ducts at a low pressure because of the low flow resistance and it therefore escapes to only a small extent through the intermediate space between the blade root and rotating gas turbine disk. By this means, the coolant losses are minimized and the coolant is utilized in an optimum manner.
Because the distribution space has a configuration rounded in the manner of an ellipsoid, the cooling air can be fed particularly advantageously to the supply ducts. In this arrangement, the distribution space is preferably configured in the form of a semi-ellipsoid. Its base area also corresponds to the maximum cross section of the ellipsoid and, in the case of a gas turbine blade/vane inserted in a disk groove, is bounded by the disk. The side surfaces of the semi-ellipsoid, and also the transitions between the side surfaces, have a rounded configuration. This simple geometry can be easily manufactured and reliably prevents the formation of dead zones in which the coolant introduced comes to rest. Due to the absence of edges, only slight eddying, which leads to negligible flow losses, occurs on the walls of the distribution space. The ellipsoid-type shape makes it possible to direct the coolant supply in a specific manner to the supply ducts adjacent to various regions of the ellipsoid.
A further optimization of the coolant flow is achieved by the rounded or beveled inlet openings meeting one another or being adjacent to one another in a manner which optimizes the flow. Optimized in terms of flow means that the flow deflections necessary due to the position of two inlet openings relative to one another or due to the position of the distribution space and an inlet opening relative to one another take place with the smallest possible amount of flow eddying. In particular, this takes place because the edges, which occur due to the meeting of the respective curvatures of the inlet openings, are in turn rounded off. The optimization of the shape preventing flow eddying is produced in the casting process by the employment of the rounded, one-piece cast core in a manner which can be individually matched without reworking to the requirements set for a certain type of gas turbine.
A predetermined supply of coolant can be easily adjusted by the cross section of the feed duct and the local changes to the cross sections of the distribution space being matched to the cross sections of the outlet openings located downstream. The cross-sectional changes to the height and width of the distribution space correspond, for example, to the shape of a semi-ellipsoid. The transitions between the inlet openings or around the inlet openings are designated as transition cross sections. The rounding or beveling of the inlet openings produces a larger inlet opening cross section directly at the distribution space and this cross section is then reduced again on transition to the supply duct. The feed duct has an essentially constant cross section but it can also be rounded or beveled in order to improve the flow properties, thus increasing the cross section in the direction toward the distribution space. The cross sections described are matched to one another, i.e. predetermined cross-sectional relationships are taken into account in the matching of the coolant supply. This is necessary if, for example, an increased coolant requirement exists because of a high operating temperature or because of special configurations of the internal cooling system in a gas turbine blade/vane, which configurations require high coolant pressures or exhibit a high leakage rate.
In the case of different coolant requirements at different locations in the internal cooling system, it is advantageous for a plurality of supply ducts to be present with different cross sections and transition cross sections of the inlet openings, which transition cross sections are respectively matched to the differ-ent cross sections. In this way, the coolant can be individually matched to the coolant requirements of the different regions of the gas turbine blade/vane. By this, the coolant consumption is reduced to the necessary extent. The manufacture of the supply ducts of different sizes or the manufacture of cross sections of different sizes is possible in one casting manufacturing process. It is only necessary to match the diameter of the core rib to this requirement.
In order to obtain a large distribution space with reduced flow eddies, it is advantageous for the lowest longitudinal rib of the blade root, which is nearest to the axis of rotation of the gas turbine, to extend along a principal axis of the gas turbine blade/vane. The blade root is held, by way of its longitudinal ribs, on undercuts of the disk groove into which it is inserted. The distribution space for the cooling medium is accommodated in the lowest longitudinal rib. In order to achieve the largest possible distribution space, and therefore little eddying of the coolant, the blade root according to the invention is lengthened in the region of the lowest longitudinal rib. This lengthening takes place along the principal axis of the gas turbine blade/vane i.e. at right angles to the periphery of the disk when the gas turbine blade/vane has been inserted. Due to the lengthened configuration of the lower longitudinal rib, the stability of the holding appliance in the blade root is further ensured and the rib can be easily lengthened in the manufacturing process of the gas turbine blade/vane by the core root of the casting core having a thicker configuration.
For the manufacture of the gas turbine blade/vane, in particular for the subsequent machining of the blade root and for ensuring adequate stability, it is advantageous for the inlet openings of the supply ducts to be located at the level of the transition flank between the lowest longitudinal rib and the longitudinal rib located above it. This ensures that the region of the distribution space is only surrounded by the lowest longitudinal rib. A transition flank, whose slope ensures secure holding of the blade root of the gas turbine blade/vane in the undercut of the disk is provided, is located between two longitudinal ribs. The arrangement proposed for the inlet openings of the supply ducts ensures that subsequent work on the blade root after the casting process can take place in a defined region without the blade/vane being damaged, the region of the distribution space being located in each case within the lowest longitudinal rib. The lengthening of the longitudinal rib can therefore be almost arbitrarily adjusted.
The object directed toward a casting appliance for the manufacture of a gas turbine blade/vane with a distribution space is achieved, for example, by an appliance for casting a gas turbine blade/vane having a casting core. It further preferably has core ribs forming the supply ducts, the casting core having a core root forming the distribution space. The core ribs are preferably formed in one piece with that core root, with a continuous transition being present from the core root to the core ribs.
In addition to an outer shell, the casting appliance has an inner casting core. The casting core is used when casting the gas turbine blade/vane in order to keep a predetermined, inner region of the gas turbine blade/vane free from cast material. The region kept free comprises the inner cooling system, the supply ducts and the distribution space. The supply ducts are kept free by elongated extensions of the casting core, the so-called core ribs. The distribution space is formed by a region which is widened relative to the core ribs and has a certain thickness and height, the so-called core root. The core root is configured in one piece with the core ribs. The one-piece configuration of the two parts of the casting core permits a rounded configuration of the transition between the supply ducts and the distribution space.
The rounded configuration of the transition between the supply ducts and the distribution space always occurs in the same manner, as specified by the shape of the casting core. This permits exact maintenance of predetermined dimensions. It permits desired dimensions of the internal cooling system of the gas turbine blade/vane to be ensured in such a way that they can be reproducibly adjusted for a complete series of gas turbine blades. This provides a basis for a low-cost and reliable manufacture of internally cooled gas turbine blades/vanes.
Because the casting core is configured in one piece, it is very stable with respect to the deformation forces which appear due to the solidification of the melt.
The transition from the core root to the core ribs is designed, in such a way that it takes place continuously in each case, by the cross section being preferably continuously increased from the core ribs to the core root. Because of the continuous transition from the core ribs into the core root, no reworking of the inlet openings of the supply ducts is necessary after the casting process in order to ensure a low flow resistance. This correspondingly dispenses with one operational step in the manufacture of the gas turbine blade/vane.
It is advantageous for the core ribs to merge into the core root with increasing cross section, which core root has a thickness which is larger than the thickness of the core ribs. This permits an additional substantial reduction in the flow resistance of the coolant flow.
A further improvement to the flow properties of the transition from the distribution space to the supply ducts is provided by the rounded core ribs running out into a curved surface which ends in the core root. This surface forms a throat, which is provided before the actual inlets to the supply ducts and which supports a continuous and low-eddy deflection of the coolant flow into the supply ducts. In addition, such a casting core is simpler to manufacture and can also be calculated more satisfactorily with respect to its flow properties.
The task directed toward a method of manufacturing a gas turbine blade/vane, using an appliance as described for the casting, is achieved by the distribution space and the supply ducts being cast using the one-piece casting core.
Due to the use of the one-piece casting core, the casting process is dimensionally more accurate and, at the same time, less time-consuming, because the individual parts of the casting core can be installed jointly. With this method, the distribution space no longer needs to be subsequently recessed mechanically. This complicated measure, which has essentially to be carried out manually, represents a time-consuming and costly step in the manufacture of a gas turbine blade/vane with distribution space. The use of the one-piece casting core, as proposed, now makes this process superfluous. In addition, the dimensions, and therefore the coolant flow through the inlet openings of the supply ducts and the distribution space, can be reproducibly adjusted.
If, however, further changes to the distribution space and/or to the inlet openings of the supply ducts are still necessary and/or desirable, the distribution space can be mechanically reworked as a supplementary measure. As compared with the usual mechanical working, this is simplified by the fact that the major part of the material to be removed is already lacking due to the casting process. Only small corrections, which involve little manufacturing complication, have therefore to be carried out.